I've been trying out Top Hat in my Criminal decks recently, and have been surprised at how impressive it's been.
A common scenario for Criminal decks in the Netrunner late game, especially when playing against combo decks (which Criminals are often weak to), is that they have a lot of money, but no servers to use it on – HQ is too well-guarded to get into repeatedly and you can't trash operations there anyway, and the remotes are either empty or full of defensive upgrades. In this situation, if things don't change, the Corp is eventually going to draw into the other half of their combo, either via clicks or perhaps with cards like Rashida Jaheem. The vulnerable server in this setup is normally R&D – against Criminal, it's common for Corps to dedicate most of their defences to HQ, and hope that R&D accesses get blocked by ICE or a Hedge Fund or the like. As long as the Corp is "bulk-drawing", you can't R&D lock them with only basic runs, so they often don't mind too much that most of their ICE went into defending HQ (and the remote, if the deck needs one).
Top Hat papers over that gap really well – if you're in a situation where R&D runs are cheap, but you have nothing much to do with your clicks, it lets you establish a very strong R&D lock (or alternatively, just get a lot of random accesses to hope to snipe the last few points – if you're playing a Criminal deck that runs a lot, you're normally on 3-5 agenda points by this stage in the game). You run R&D, and access the top card. Then you run R&D, and access the second card, and so on. The idea is to remember how far into R&D you've gotten, count the cards that the Corp draws (so you know how deep into R&D you've looked already), and continue your R&D runs where you left off. As long as you can run often enough, you can ensure that the Corp never draws an agenda, so every point that turns up will go into your score area rather than the Corp's (which is very important if they're loading up on Audacity or Biotic Labor).
Although this strategy might seem expensive – and for a Shaper, it would be! – the release of Cezve has meant that repeated centrals running is now well within the reach of many Criminals (except when playing against glacier). As such, the main effect that playing Top Hat has is to force the Corp to put a lot of ICE on R&D, and then pay to rez it, two things that generally aren't high priority for Corps playing against Criminal. Stretching the Corp's resources too thinly and forcing them to cover too many servers is how Criminals win games, so it's possible to get a surprising amount of benefit from one card slot that costs 0 and 1 influence.
Top Hat also has a fringe use as a tech card, in that it makes it possible to run R&D, and access cards in it without "breaching" R&D or accessing cards in its root. This dodges some defensive upgrades, notably Prisec and Mwanza City Grid. It'd take a very weird metagame for this use as a tech card to become a reason on its own to play Top Hat (even though the main users of Prisec and Mwanza City Grid, Ob Superheavy Logistics and Jinteki: Personal Evolution, are quite popular at the moment, the metagame hasn't reached that level of distortion yet). However, it's a bonus, that does help contribute to the strength of the card.
What about combos? The combo with Insight is obvious, but not really where a Criminal wants to be spending influence – being able to look at four cards in R&D and then run in to steal one (for two cards, three influence, and ) is only a slightly better effect than simply just running in with The Maker's Eye (which is one card, two influence, and , 2). And The Maker's Eye typically isn't making the cut in Criminal lists (or even Shaper lists) nowadays – even Ken can often find better uses for the card slots.
However, there's another combo, with Möbius, which I have been trying out – it's probably unplayable outside Ken decks, but seems marginally playable there. Ken decks need a huge critical mass of run events to work (and Möbius qualifies), and are often facing an undefended R&D turn 1 (a situation in which Möbius is probably the best economy card in the game, gaining 5 for a click and seeing the top card of R&D twice – this is a better rate of return than even Carpe Diem). As such, Möbius has obvious early-game advantages for Ken, but suffers from falling off somewhat in the late game because it's hard to get benefit from both runs (and yet you need to succeed at both in order to get the 4 from Möbius). Top Hat helps to make Möbius playable by giving it a late-game purpose as well – if you're trying to R&D lock with repeated R&D runs and accessing a different card each time, making two R&D runs in the same turn is reasonable, and making the pair of runs , 4 cheaper is definitely worth a card (and another , 1 cheaper if it triggers Ken's ID ability and Swift's refund). It's also always fun to see your opponent reading the cards you're playing.
There's probably also a viable combo with Find the Truth (build your own R&D Interface with two 0-cost cards!), but I haven't tested this one myself so I don't know how well it would work.
So is Top Hat worth it in Criminal? I think it's a serious competitor for a deck slot in some Criminal decks, but I'm not convinced that it'll actually win that competition. It definitely has an effect that many Criminal decks want, and that they find hard to get by other means; and it helps to shore up some common match-ups (especially fast-advance and combo decks) that Criminals often find difficult to win. The main question is simply as to whether you can find another 45 cards that give a larger benefit to your deck than the rather situational benefit that you get from a Top Hat, and that's going to depend a lot on how the deck is designed, what its economy looks like, and the like. (Top Hat seems to be better in decks with a mix of an event economy and Cezve – this economy mix can get up to high credit totals in the mid-to-late game and is good at repeatedly running R&D, but will eventually run out of credits if the game goes very long, and thus needs some way to close games out.) You also need to check whether the deck can use the similar (but more expensive) Stargate instead – Stargate has a better effect if you can get it installed, but many decks can't afford the influence, or the install hit, or (in particular) the memory cost. Top Hat can thus be seen as a "baby Stargate" – a similar but worse effect, but one that's much easier to include in a deck and that may be sufficient to patch a Stargate-shaped hole that you can't afford an actual Stargate to fill.
As such, for many Criminal decks, I suspect that this is a card to try out, and eventually reject – but it's hard to know whether it's worth rejecting without trying it, and it seems to slot into some decks really neatly.
